As an iron core of a distribution transformer or the like may be used a wound iron core using a Fe—B—Si-based amorphous alloy thin strip. As a material used for the wound iron core, for example, JP-A-554-148122, JP-A-555-094460 and JP-A-557-137451 disclose an amorphous alloy thin strip with a thickness of several tens μm prepared by injecting a iron-based molten alloy based on Fe and added with B, Si and the like onto a surface of a high-speed rotating cooling roll to perform rapid solidification.
The Fe—B—Si-based amorphous alloy thin strip has a feature that an iron loss is low compared to a grain-oriented electrical steel sheet prepared by utilizing conventional secondary recrystallization, but is low in the saturated magnetic flux density. Hence, a design magnetic flux density must be decreased so that there are such problems that the transformer is made large and a greater amount of copper wire for the coil is required.
Therefore, a technique of increasing a ratio of Fe content in an amorphous alloy to enhance a saturated magnetic flux density to thereby make a design magnetic flux density large is developed, which provides a certain improvement effect. However, since the alloy having a higher ratio of Fe content lowers an amorphous stability, it is difficult to stably provide a low iron loss. Also, there is a problem that iron loss measured at a wound iron core state is increased compared to iron loss measured on a raw steel material, that is, a so-called “building factor” is large.
It could therefore be helpful to provide a Fe—B—Si-based amorphous alloy thin strip capable of stably providing a high magnetic flux density and low iron loss wound iron core.